Hydrodynamic Circumferential Seal System for Large Translations

ABSTRACT

A circumferential seal system for sealing a high pressure region from a low pressure region separated by a runner with an outer circumferential surface and a seal ring disposed about the outer circumferential surface is described. The seal system includes a plurality of groove sets separately disposed along the outer circumferential surface. Each groove set further includes at least two grooves. At least one groove within each groove set exerts a lifting force via a fluid from the high pressure region onto the seal ring as the runner translates with respect to the seal ring along an axis substantially perpendicular to the rotation of the runner. The continuous feed of fluid onto the seal ring ensures a thin film between the seal ring and the runner regardless of their relative arrangement during axial excursions of the runner resulting from conditions within a turbine engine.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims priority from PatentCooperation Treaty Application No. PCT/US2009/055103 filed Aug. 27,2009, entitled Hydrodynamic Circumferential Seal System for LargeTranslations, which is hereby incorporated in its entirety by referencethereto.

FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

None.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention generally relates to a circumferential seal between a sealring and a runner capable of large axial translations with respect tothe seal. Specifically, the invention includes a plurality ofhydrodynamic grooves disposed along the outer circumference of a runnereither parallel or diagonal to the direction of rotation. Hydrodynamicgrooves are further arranged into separate and distinct groove setsabout the runner. Each groove set includes at least two grooves whicheither separately or jointly exert a hydrodynamic lifting force onto theinner diameter of the seal ring regardless of their position relative tothe runner.

2. Background

There are many applications wherein housings are provided with aplurality of interior sections having rotating parts passing therethrough, wherein one of the interior housing sections must be isolatedfrom another by means of a seal system. In gas turbine applications, forexample, it is critical that the lubricant contained within a lubricantchamber of the housing be sealed from an adjacent fluid or gas side ofthe seal. This is especially true along a rotatable shaft which oftenpasses from the lubricant side of the seal to the fluid side. In anaircraft engine, these sump seals are used to separate ambient areas ofhigh pressure air, e.g. the gas side, from an oil wetted area at lowerambient pressures, e.g. the lubricant side. These seals prevent oilleakage from the lower pressure compartment and minimize the flow rateof hot air from the high pressure area to the oil wetted compartment.

Leakage of liquids from the lubricant side into the gas side adverselyaffects performance of the equipment where a seal is used. In the caseof an aircraft engine, oil leakage across the seal into a hot air sidemay cause oil coking or an engine fire. More specifically, when an oillubricant is used, mixing the oil with the gas could result in formationof oil coke, a byproduct of oil heated to an elevated temperature, whichchemically alters the oil and is detrimental to the gas turbine. Oilcoke can foul seal surfaces reducing the integrity of the seal andpreventing proper bearing lubrication within the lubricant sump.Accordingly, it is important in similar applications, not just aircraftengines, that the lubricant be isolated within a lubricant sump and thatthe seal around the rotating shaft not allow the lubricant to escape thesump. Seals in such applications may comprise either circumferentialseals or face-type seals; however, circumferential shaft seals are themost widely used under the above conditions.

The term circumferential seal broadly describes a generic type ofsealing device used widely, inter alia, on aircraft engine applications.FIGS. 1 a and 1 b show a standard seal assembly 1 disposed about arunner 2 between a low pressure region 3 and a high pressure region 4.The seal assembly 1 supports a seal ring 6 about the runner 2 andtypically includes a seal housing 5, a retaining ring 7, a back plate 8,a plurality of compression springs 9 disposed about the seal ring 6, agarter spring 10, a cavity 43, and an anti-rotation pin 14. A lift pad11 along the seal ring 6 forms a circumferential seal with the runner 2at the sealing radius 15 and could include a dead-end bore groove 26 anda bore dam 13 to improve sealing performance. A second surface 12 alongthe seal ring 6 provides a face seal with the seal housing 5.

FIGS. 2 a and 2 b show face and bore views, respectively, of a standardring segment 16. A plurality of ring segments 16 typically comprises aseal ring 6. Each ring segment 16 is composed primarily of carbon and/orgraphite and is arranged circumferentially around a runner 2 to form acontinuous, relatively stationary seal ring 6. Each ring segment 16includes a tongue 17 and a socket joint 18 which overlap between twoadjacent ring segments 16 to restrict leakage. The related arts describesealing rings with one or more pockets or similar structures along thebore thereof. The related arts do not provide such pockets along theouter circumferential surface 19 along the runner 2 shown in FIG. 1 a.

Most current circumferential seals utilize a variant of thecircumferential seal illustrated in FIGS. 1 a, 1 b, 2 a, and 2 b toaddress the sealing requirements between a low pressure liquidcompartment and a high pressure gas compartment. In one example, Popediscloses in U.S. Pat. No. 5,145,189 a sealing ring with a shallowgroove which redirects pressurized air to a plurality of deeper ventgrooves. In another example, Hwang discloses in U.S. Pat. No. 6,145,843a sealing ring with shallow lift pockets in fluid communication with ahigh pressure region by a plenum chamber.

The position of grooves along the bore of a sealing ring is problematic,particularly in higher-performance turbine engines. First, sealing ringsare typically composed of carbon graphite and as such are prone tosurface wear which compromises shallow hydrodynamic grooves along aring. Second, the design of and operating conditions within such enginesoften cause the runner to widely translate along the axis of the engine.For example, axial translations in the range of a quarter of an inch arepossible by a runner in some applications. Large relative movementbetween a runner and a sealing ring with conventional groovearrangements aligned at a single axial location allow fluid within thegrooves to vent in an uncontrolled fashion. The result is a reduction orloss of the hydrodynamic lifting force exerted by the grooves onto therunner. A less robust lifting force is more likely to allow contactbetween the runner and sealing ring. Any such contact wears the boresurface along the sealing ring, reducing the depth and performance ofthe grooves over time.

As is readily apparent from the discussions above, the related arts donot include a circumferential seal which avoids the performance problemsassociated with seal systems that include a runner capable of largeaxial translations and a sealing ring with grooves along its bore.

Accordingly, what is required is a circumferential seal which maintainsthe lift properties between a seal ring and a seal runner during largeaxial excursions of the seal runner.

SUMMARY OF THE INVENTION

An object of the invention is to provide a circumferential seal whichmaintains the lift properties between a seal ring and a seal runnerduring large axial excursions of the seal runner.

In accordance with an embodiment of the invention, the circumferentialseal system seals a high pressure region from a low pressure regionseparated by a runner with an outer circumferential surface and a sealring including a plurality of ring segments disposed about the outercircumferential surface. The seal system includes a plurality of groovesets separately disposed along the outer circumferential surface. Eachgroove set includes at least two grooves. At least one groove withineach groove set exerts a lifting force via a fluid from the highpressure region onto the seal ring as the runner translates with respectto the seal ring along an axis substantially perpendicular to therotation of the runner.

In other embodiments, each groove set could include grooves which arediagonal or substantially parallel to the rotational direction of therunner.

In yet other embodiments, each groove set could include a feed groovewhich communicates a fluid into the grooves comprising the set. The feedgroove could be perpendicular or at an angle with respect to thegrooves.

In still other embodiments, grooves between adjacent groove sets coulddiffer in number and arrangement so that grooves are offset along theouter circumferential surface.

In further embodiments, the grooves within each groove set could havedifferent lengths or could be positioned along the outer circumferentialsurface so that at least one groove ensures communication of a liftforce onto the bore of the seal ring before translation commences and atleast one other groove ensures communication of a lift force onto thebore of the seal ring as the runner translates.

In some further embodiments, alternating groove sets could communicate alift force onto the seal ring or at least one groove set couldcommunicate a lift force onto each ring segment.

Several advantages are offered by the invention described herein. Theinvention ensures at least one groove within each groove set is disposedalong the overlay region between each segment of a seal ring and arunner as the runner translates with respect to the seal ring so as tocontinuously communicate a hydrodynamic lifting force onto each segment.The continuous feed of pressurized fluid onto the seal ring furtherensures a thin film between the seal ring and the runner regardless oftheir relative arrangement during axial excursions of the runner causedby temperature and other conditions immediately adjacent to the sealsystem. The invention places the hydrodynamic grooves along the outerdiameter of the runner which is inherently more resistant to wear thanthe seal ring, thereby increasing seal life.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional aspects, features, and advantages of the invention will beunderstood and will become more readily apparent when the invention isconsidered in the light of the following description made in conjunctionwith the accompanying drawings.

FIG. 1 a is a cross-sectional view illustrating a prior artcircumferential seal assembly disposed about a runner within a turbineengine.

FIG. 1 b is an enlarged cross-sectional view further illustratingfeatures of the prior art circumferential seal assembly in FIG. 1 a.

FIG. 2 a is a side elevation view illustrating a ring segment from aprior art circumferential seal.

FIG. 2 b is an outward radial view illustrating tongue and socket jointfeatures along the ring segment in FIG. 2 a.

FIG. 3 is a cross-sectional view illustrating a circumferential sealassembly disposed about a runner in accordance with an embodiment of theinvention.

FIG. 4 is an enlarged cross-sectional view illustrating placement ofhydrodynamic grooves along the outer circumferential surface of therunner in FIG. 3 which are substantially parallel to the rotationaldirection in accordance with an embodiment of the invention.

FIG. 5 is an inward radial view illustrating arrangement of grooves intogroove sets along the outer circumferential surface of a runner in FIG.4 wherein each groove set includes substantially parallel groovescommunicating with and perpendicular to a feed groove in accordance withan embodiment of the invention.

FIG. 6 is a cross-sectional view illustrating the profile of ahydrodynamic groove with feed groove along the runner in FIG. 5 inaccordance with an embodiment of the invention.

FIG. 7 is an inward radial view illustrating arrangement of grooves intoa groove set along the outer circumferential surface of a runner whereinthe groove set includes parallel grooves communicating with an obliquelydisposed feed groove in accordance with an embodiment of the invention.

FIG. 8 is an enlarged cross-sectional view illustrating placement ofgrooves along the outer circumferential surface of the runner in FIG. 3in which the grooves are diagonal to the rotational direction of therunner in accordance with an embodiment of the invention.

FIG. 9 is an inward radial view illustrating arrangement of grooves intogroove sets along the outer circumferential surface of a runner in FIG.8 wherein each groove set includes substantially parallel groovesdisposed at an angle with respect to the rotational direction of therunner in accordance with an embodiment of the invention.

FIG. 10 is a cross-sectional view illustrating the profile of ahydrodynamic groove along the runner in FIG. 9 in accordance with anembodiment of the invention.

FIG. 11 a is an inward radial view illustrating arrangement of groovesinto groove sets along the outer circumferential surface of a runnerbefore translation thereof wherein each groove set includessubstantially parallel grooves disposed at an angle with respect to therotational direction of the runner and the seal ring includes a bore damand a bore groove in accordance with an embodiment of the invention.

FIG. 11 b is an inward radial view illustrating arrangement of groovesets with respect to the seal ring after translation of the runner inFIG. 11 a.

FIG. 12 is a plot illustrating an exemplary pressure field within ahydrodynamic groove in accordance with an embodiment of the invention.

FIG. 13 is a schematic diagram illustrating the forces about a seal ringwith hydrodynamic grooves disposed along the outer circumferentialsurface of a runner in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to several preferred embodiments ofthe invention that are illustrated in the accompanying drawings.Wherever possible, same or similar reference numerals are used in thedrawings and the description to refer to the same or like parts orsteps. The drawings are not to precise scale.

Referring now to FIGS. 3-4, the circumferential seal system is shownwithin a seal assembly 1 having a seal ring 6 therein which is adjacentto and disposed about a runner 20. The seal assembly 1 and seal ring 6could include a variety of designs known within the art. As such, thecircumferential seal system described herein could be applied to a widevariety of engines with rotating elements which traverse compartmentsrequiring isolation from one another.

Furthermore, embodiments of the circumferential seal system describedherein are applicable to both low and reverse air pressure conditionswithin an engine. During certain flight conditions in advanced gasturbine engines, the air pressure could be higher on the sump side thanthe seal chamber side causing significant oil leakage from the sump. Thehydrodynamic grooves generate higher air pressure than the sump duringpressure reversals, thus preventing the oil from leaking past the boredam 13. As such, air continues to flow from the seal chamber side to thesump during pressure reversals when the pressure differential isnegative.

In the instant invention, the runner 20 includes a plurality ofpocket-like grooves 21 recessed along its outer circumferential surface19. The grooves 21 could reside directly within the structure composingthe runner 20 or along a coating 22 applied onto the outercircumferential surface 19.

In some embodiments, it might be advantageous to have the coating 22recessed within a step 37 along the outer circumferential surface 19.The coating 22 is preferred to be a hard, wear resistant materialapplied via methods understood in the art. For example, the coating 22could be composed of a tungsten carbide composition flame sprayed ontothe outer circumferential surface 19 to form a uniform layer with athickness from 0.003 to 0.005 inch. Grooves 21 and/or step 37 could bemachined, molded, or formed into the runner 20 or coating 22 via methodsunderstood in the art.

Referring now to FIGS. 4-5, the grooves 21 are arranged to form distinctgroove sets 24 a-24 c about the circumference of the runner 20 separatedby a space 42. However, it is possible in some embodiments for adjacentgroove sets 24 a-24 c to overlap or be interdigitated in anon-contacting arrangement when the second end 40 of the grooves 21within each groove set 24 a-24 c is disposed in an angular and/or offsetarrangement. While three groove sets 24 a-24 c are shown in FIG. 5, itis understood that a plurality of such structures could reside along thecircumference of the runner 20. As such, the total number of groove sets24 a-24 c is application and design dependent.

The grooves 21 within each groove set 24 a-24 c could have the same ordifferent lengths and could include a variety of non-parallel andparallel arrangements. Each groove set 24 a-24 c separately directsfluid from the high pressure region 4 onto the seal ring 6. Furthermore,each groove 21 within a groove set 24 a-24 c could separately directfluid onto the seal ring 6.

Referring again to FIG. 5, the grooves 21 are arranged in asubstantially parallel configuration along the outer circumferentialsurface 19 of the runner 20. The grooves 21 are separated by a space 44which could vary along a groove set 24 a-24 c and between and/or alongadjacent grooves 21. A feed groove 23 could reside along the outercircumferential surface 19 and intersect the first end 39 of each groove21 so as to form a continuous pathway along the feed groove 23 and eachgroove 21 within a groove set 24 a-24 c. The feed groove 23 couldintersect the grooves 21 in a perpendicular arrangement, as shown inFIG. 5, or at an angle 36, as represented in FIG. 7. The inlet 41 ofeach feed groove 23 is preferred to be oriented towards the highpressure region 4 to facilitate communication of a fluid there from intothe feed groove 23 and thereafter into each groove 21. In preferredembodiments, fluid between the seal ring 6 and runner 20 could bleedinto the low pressure region 3 in a controlled fashion.

The total number of groove sets 24 a-24 c is determined in part by thedimensions of the seal ring 6 and runner 20, the number of ring segments16, the length of each ring segment 16, the number and angulararrangement of grooves 21 within each groove set 24 a-24 c, the length,depth and width of each groove 21, the number of grooves 21 required todirect fluid under the seal ring 6 or each ring segment 16 to maintainthe desired lifting force between the runner 20 and seal ring 6, theoverlap or offset of grooves 21 between adjacent groove sets 24 a-24 c,and the maximum translation distance of the runner 20.

The number of grooves 21 within each groove set 24 a-24 c along theouter circumferential surface 19 could be the same or different. In FIG.5, a groove set 24 b with three grooves 21 is shown disposed between apair of groove sets 24 a, 24 c with two grooves 21; however, otherconfigurations are possible. In another more generalized example, thenumber of grooves 21 could vary between interposed groove sets 24 a-24 csuch that a groove set 24 b with x number of grooves 21 is disposedadjacent to groove sets 24 a, 24 c with x+y grooves 21, where x and yare whole numbers greater than 0.

The grooves 21 between groove sets 24 a-24 c could be offset asrepresented in FIG. 5 to further ensure communication of fluid onto theseal ring 6 along its entire translation path. The degree of offset isdesign dependent and could allow for no or partial overlap between oneor more grooves 21 in adjacent groove sets 24 a-24 c.

Axial translation of the runner 20 could result from non-steady stateconditions, temperatures, or other influences. In general terms, thistranslation is substantially parallel to the axis of rotation of therunner 20 or substantially perpendicular to the rotation of the runner20, as represented in FIG. 5. For explanation purposes, the term overlayregion represents the area along the outer circumferential surface 19immediately below a seal ring 6 or ring segment 16. The initial overlayregion 33 represents the configuration between the seal ring 6 or ringsegment 16 and runner 20 at startup. In this example, the rightmostgroove 21 in the outer groove sets 24 a, 24 c and the right two grooves21 in the inner groove set 24 b could be covered by the seal ring 6 orring segment 16. As such, the identified grooves 21 could communicatefluid onto the seal ring 6 or ring segment 16. After the runner 20translates to its maximum translation distance 35, the seal ring 6 orring segment 16 covers the runner 20 along the area represented by thefinal overlay region 34. In this position, the leftmost groove 21 in theouter groove sets 24 a, 24 c and the left two grooves 21 in the innergroove set 24 b could be covered by the seal ring 6 or ring segment 16.As such, the identified grooves 21 could communicate fluid under theseal ring 6 or ring segment 16. For translations between the initial andfinal overlay regions 33, 34, it is possible for other combinations ofgrooves 21 within one or more groove sets 24 a-24 c to communicate fluidpressure under the seal ring 6 or ring segments 16. The maximumtranslation distance 35 could allow some or no overlap between theinitial and final overlay regions 33, 34.

Referring now to FIGS. 4-6, the profile of an exemplary groove 21 andfeed groove 23 are shown. The groove 21 is represented as a structure ofsubstantially linear extent with a length 28, uniform depth 27 anduniform width 31; however, it is possible for the depth 27 and width 31to vary along the length 28 of the groove 21 to form a tapered or otherprofile. It is also possible for the groove 21 to be non-linear orarcuate along its length 28. The second end 40 of the groove 21 couldterminate as a triangular, rectangular, flat, or circular structure, thelatter represented in FIG. 5. Exemplary, non-limiting dimensions include0.000010 to 0.010 inches for the depth 27, 0.010 to 1.000 inches for thewidth 31, 0.100 to 10.000 inches for the length 28, and 0.010 to 1.000inches for the space 44.

The feed groove 23 is also represented as a structure of substantiallylinear extent with a length 32, uniform width 30, and depth 29; however,it is also possible for the depth 29 to be uniform along the length 32and/or the depth 29 and width 30 to vary along the feed groove 23 toform a tapered or other profile. It is also possible for the feed groove23 to be non-linear or arcuate along its length. While the feed groove23 is shown with a curved profile, other shapes are possible. Exemplary,non-limiting dimensions include 0.000010 to 0.010 inches for the depth29, 0.010 to 1.000 inches for the width 30, and 0.100 to 10.000 inchesfor the length 32.

Referring now to FIGS. 8 and 9, the grooves 21 are arranged to formdistinct groove sets 24 a-24 c along the circumference of the runner 20with non-contacting overlap of grooves 21 between adjacent groove sets24 a-24 b, 24 b-24 c. While three groove sets 24 a-24 c are shown inFIG. 9, it is understood that a plurality of such structures wouldreside about the circumference of the runner 20. As such, the totalnumber of groove sets 24 a-24 c is application and design dependent, asdescribed herein.

The runner 20 includes a plurality of pocket-like grooves 21 recessedalong its outer circumferential surface 19. The grooves 21 could residedirectly within the structure composing the runner 20 or along a coating22 applied onto the outer circumferential surface 19. In someembodiments, it might be advantageous to have the coating 22 recessedwithin a step 37 along the outer circumferential surface 19. The coating22 is preferred to be a hard, wear resistant material, as describedherein, fabricated via methods understood in the art.

The grooves 21 within each groove set 24 a-24 c could have the same ordifferent lengths and could include a variety of non-parallel andparallel arrangements. Each groove set 24 a-24 c separately directsfluid from the high pressure region 4 onto the seal ring 6. Furthermore,each groove 21 within a groove set 24 a-24 c could separately directfluid under the seal ring 6 or segment 16.

In FIG. 9, the grooves 21 are arranged in a substantially parallelconfiguration along the outer circumferential surface 19 of the runner20. The grooves 21 are separated by a space 44 which could vary alongthe groove set 24 a-24 c or between and/or along adjacent grooves 21. Inthis embodiment, the grooves 21 are set at an angle 25 with respect tothe rotation direction of the runner 20 so that the first end 39 of eachgroove 21 is generally aligned along one side of the outercircumferential surface 19 and oriented towards the high pressure region4. This arrangement allows communication of a fluid from the highpressure region 4 into each groove 21. The second end 40 of each groove21 is oriented towards the low pressure region 3 so as to terminate eachgroove 21 at a different distance from the high pressure region 4. Thisarrangement ensures one or more second ends 40 within a groove set 24a-24 c communicate fluid onto the seal ring 6 or ring segment 16 duringtranslation of the runner 20. In preferred embodiments, fluid betweenthe seal ring 6 and runner 20 could bleed into the low pressure region 3in a controlled fashion. The total number of groove sets 24 a-24 c isapplication and design dependent, as described herein.

The number of grooves 21 within each groove set 24 a-24 c along theouter circumferential surface 19 could be the same or different. In FIG.8, each groove set 24 b is shown with three grooves 21 of varyinglength; however, other configurations are possible including withoutlimitation grooves 21 with non-parallel sides forming a point shaped ortruncated end.

In this embodiment, the initial overlay region 33 could be theconfiguration between the seal ring 6 or ring segment 16 and runner 20at startup. In one example, the seal ring 6 or ring segment 16 couldoverlay a portion of the two rightmost grooves 21 so as to cover thesecond ends 40 thereof. As such, the identified grooves 21 couldcommunicate fluid onto the seal ring 6 or ring segment 16. After therunner 20 translates to its maximum translation distance 35, the sealring 6 or ring segment 16 could cover the runner 20 along the arearepresented by the final overlay region 34. In this position, theleftmost grooves 21 within the groove sets 24 a-24 c could overlay theseal ring 6 or one or more ring segment 16 so as to cover the secondends 40 thereof. As such, the identified grooves 21 could communicatefluid onto the seal ring 6 or the ring segments 16. For translationsbetween the initial and final overlay regions 33, 34, it is possible forat least the center groove 21 or other combinations of grooves 21 withinone or more groove sets 24 a-24 c to communicate fluid onto the sealring 6 or ring segments 16. The maximum translation distance 35 couldallow some or no overlap between the initial and final overlay regions33, 34.

Referring now to FIGS. 9-10, the profile of an exemplary groove 21 isshown. The groove 21 is represented generally as a linear structure witha length 28, depth 27 and width 31 of uniform dimensions; however, it ispossible for the depth 27 and width 31 to vary along the length 28 ofthe groove 21 or to form various profiles. It is also possible for thegroove 21 to be non-linear or arcuate along its length 28. The secondend 40 of the groove 21 could terminate as a triangular, rectangular,circular, or flat structure, the latter two represented in FIGS. 9 and11 a, respectively. Exemplary, non-limiting dimensions include 0.000010to 0.010 inches for the depth 27, 0.010 to 1.000 inches for the width31, 0.100 to 10.000 inches for the length 28, and 0.010 to 1.000 inchesfor the space 44.

Referring now to FIGS. 11 a-11 b, another embodiment of the invention inFIGS. 8-9 is shown including a plurality of grooves 21 arranged intoseparate and non-overlapping groove sets 24 a-24 c disposed in asubstantially parallel configuration along the outer circumferentialsurface 19 of the runner 20. In this embodiment, the grooves 21 are setat an angle 25 with respect to the rotation direction of the runner 20so that the first end 39 of each groove 21 is generally oriented towardsthe high pressure region 4. This arrangement allows communication offluid from the high pressure region 4 into the grooves 21 depending onthe position of the seal ring 6. The second end 40 of each groove 21 isoriented towards the low pressure region 3 so as to terminate eachgroove 21 at a different distance from the high pressure region 4.Further, the first end 39 and second end 40 are truncated to form apoint such that the leftmost side of the point for the second end 40 andrightmost side of the point for the first end 39 are parallel to thesides of the seal ring 6. This arrangement ensures one or more secondends 40 within a groove set 24 a-24 c communicate fluid onto the sealring 6 or ring segment 16 during translation of the runner 20.

In this embodiment, the initial overlay region 33 could be configured sothat the lift pad 11, bore groove 26, and bore dam 13 along the sealring 6 or ring segment 16 in FIG. 1 b overlay a portion of the threerightmost grooves 21, as graphically represented in FIGS. 11 a-11 b, soas to cover the second ends 40 thereof. As such, at least the tworightmost grooves 21 could communicate fluid onto the seal ring 6 orring segment 16. After translation of the runner 20, the lift pad 11,bore groove 26, and bore dam 13 could cover the runner 20 along the arearepresented by the final overlay region 34. In this position, the twoleftmost grooves 21 within each groove set 24 a-24 c could overlay thelift pad 11 so as to cover the second ends 40 thereof. As such, theidentified grooves 21 could communicate fluid onto the seal ring 6 orthe ring segments 16. For translations between the initial and finaloverlay regions 33, 34, it is possible for the lift pad 11, bore groove26, and/or bore dam 13 to interact with one or more grooves 21 withineach groove set 24 a-24 c to communicate fluid onto the seal ring 6 orring segments 16.

In some embodiments, the length 45 of the grooves 21 could be such thatthe effective width 46 of each groove 21 is equal to or less than thewidth of at least the lift pad 11 along the seal ring 6 to cut off theflow path of fluid from the high to low pressure regions 4, 3 at somepoint during axial translations. This arrangement could prevent highpressure from entering the high pressure end of a groove 21 once it isunderneath or overlaid by the seal ring 6.

Referring now to FIG. 12, an exemplary pressure profile is shown for thefluid along the length 28 of a groove 21, assuming the groove 21 isnearly completely overlaid by a seal ring 6 or one or more ring segments16. In this example, the pressure at the first end 39 could be nearlyzero or an ambient value and steadily increase along the length 28 ofthe groove 21 to a maximum value at the second end 40. In otherexamples, the minimum pressure might occur at a location along thegroove 21 when the seal ring 6 or a ring segment 16 first overlays thegroove 21. In yet other examples, the pressure could have a non-linearprofile dependent on the interface conditions between the seal ring 6 orthe ring segment 16 and the runner 20, dimensions of one or more grooves21, and other factors.

Generally, it is desired for a seal ring 6 or one or more ring segments16 to substantially overlay the length 28 of a groove 21 so as tomaximize the lift force communicated from the runner 20 to the seal ring6 or ring segments 16. It is also possible for the groove 21 toadequately communicate a lift force onto a seal ring 6 or ring segment16 when the groove 21 is partially covered so as to overlay a regionadjacent to the second end 40. When grooves 21 within a groove set 24a-24 c are of different lengths, at least one groove within each grooveset 24 a-24 c should be sufficiently long so as to ensure a liftingforce between the runner 20 and seal ring 6 before translation of therunner 20 and at least one other groove 21 should be sufficiently longso as to ensure maintenance of a lifting force as the runner 20 alongthe translation path of the runner 20. It is also possible for thegrooves 21 to be separately located along the outer circumferentialsurface 19 so that at least one groove 21 ensures formation of a liftforce between the runner 20 and the seal ring 6 before translation andat least one other groove 21 maintains the lifting force across thetranslation path of the runner 20.

The circumferential seal systems described herein direct fluid from thehigh pressure region 4 into a plurality of groove sets 24 a-24 cseparately disposed along the outer circumferential surface 19.Thereafter, the fluid is communicated from at least one groove 21 withineach groove set 24 a-24 c onto the seal ring 6 as the runner 20translates with respect to the seal ring 6 along an axis substantiallyperpendicular to the rotation of the runner 20. This fluid forms a thinfilm which is sufficient to generate a lifting force along the seal ring6 so as to move the seal ring 6 away from the outer circumferentialsurface 19. In some embodiments, the lifting force could be generated byat least one groove 21 within at most every other groove set 24 a-24 c.

Referring now to FIG. 13, the force balance which produces thehydrodynamic operating clearance, h, between a seal ring 6 and runner 20when the instant invention is applied to the components shown in FIGS. 1a and 1 b, is graphically represented about a seal ring 6 with specificreference to forces F₁ through F₉.

Loading conditions along the axial direction generally include fourprimary components. The right side of the seal ring 6 includes force F₁produced by the high pressure region 4 and force F₂ exerted by thecompression springs 9. The left side of the seal ring 6 includes thereaction force F₃ at the interface between the seal housing 5 and sealring 6 along the second surface 12 and force F₄ produced by the pressurebreakdown over the face dam. The total magnitude of forces F₁ and F₂should exceed that of the total magnitude of forces F₃ and F₄ so as tosecure the seal ring 6 axially against the seal housing 5.

Loading conditions along the radial direction generally include fiveprimary components. The outer circumference of the seal ring 6 includesforce F₅ produced by pressurized fluid from the high pressure region 4within the cavity 43 between the seal ring 6 and seal housing 5 andforce F₆ exerted by the garter spring 10. The inner circumference of theseal ring 6 includes force F₇ resulting from high pressure surroundingthe lift pad 11, force F₈ resulting from the pressure breakdown underthe bore dam 13, and force F₉ produced by fluid directed onto the sealring 6 by the hydrodynamic grooves 21 as described herein. The totalmagnitude of forces F₅ and F₆ should be equal to or less than the totalmagnitude of forces F₇, F₈, and F₉ at steady-state conditions so thatthe seal ring 6 is maintained at a distance from the otherwise rotatingrunner 20 while minimizing flow from the high pressure region 4 to thelow pressure region 3. During non steady-state conditions, the totalmagnitude of forces F₅ and F₆ should be less than that of forces F₇, F₈,and F₉ so that the seal ring 6 is forced or pushed away from therotating runner 20 at startup and allowed to move towards and eventuallycontact the runner 20 at shutdown. The hydrodynamic seal rides on afluid film and is non-contacting for the purpose of increasing seallife, reducing heat generation, and could reduce or eliminate the needto cool the runner 20 with oil in turbine engines.

As is evident from the explanation above, the circumferential sealsystem and variations thereof maintain the sealing properties of thesystem at an interface which exhibits large relative axial translations.The invention is expected to be used within applications wherein ahousing is provided with a plurality of interior sections havingrotating parts passing there through, wherein one of the interiorhousing sections must be isolated from another by means of a sealsystem. One specific non-limiting example is a turbine engine.

The description above indicates that a great degree of flexibility isoffered in terms of the invention. Although various embodiments havebeen described in considerable detail with reference to certainpreferred versions thereof, other versions are possible. Therefore, thespirit and scope of the appended claims should not be limited to thedescription of the preferred versions contained herein.

1. A circumferential seal system for sealing a high pressure region froma low pressure region separated by a runner with an outercircumferential surface and a seal ring including a plurality of ringsegments disposed about said outer circumferential surface comprising: aplurality of groove sets separately disposed along said outercircumferential surface, each said groove set including at least twogrooves, at least one said groove within each said groove setcommunicates a fluid from said high pressure region onto said seal ringas said runner translates with respect to said seal ring along an axissubstantially perpendicular to the rotation of said runner, said fluidproducing a lift force between said seal ring and said runner.
 2. Thecircumferential seal system of claim 1, wherein said grooves within atleast one said groove set are substantially parallel.
 3. Thecircumferential seal system of claim 1, wherein each said groove setfurther includes a feed groove, said feed groove communicates said fluidinto each said groove.
 4. The circumferential seal system of claim 3,wherein said feed groove is perpendicular to said grooves within saidgroove set.
 5. The circumferential seal system of claim 3, wherein saidfeed groove is disposed at an angle with respect to said grooves withinsaid groove set.
 6. The circumferential seal system of claim 1, whereinadjacent said groove sets have different numbers of said grooves.
 7. Thecircumferential seal system of claim 6, wherein said groove sets with xsaid grooves are interposed with said groove sets with x+y said grooveswhere x and y are whole numbers greater than
 0. 8. The circumferentialseal system of claim 1, wherein said grooves between adjacent saidgroove sets are offset.
 9. The circumferential seal system of claim 1,wherein said grooves within at least one said groove set are parallel tothe rotational direction of said runner.
 10. The circumferential sealsystem of claim 1, wherein said grooves within at least one said grooveset are diagonal to the rotational direction of said runner.
 11. Thecircumferential seal system of claim 10, wherein the length of saidgrooves is such that the effective width of each said groove is equal toor less than the width of the lift surface along said seal ring toterminate the flow path of said fluid from said high pressure region tosaid low pressure region.
 12. The circumferential seal system of claim1, wherein said grooves within each said groove set are differentlengths or located along said outer circumferential surface so that atleast one said groove is sufficiently long so as to ensure said liftforce before translation of said runner and at least one other saidgroove is sufficiently long so as to ensure said lift force as saidrunner translates.
 13. The circumferential seal system of claim 1,wherein at most every other said groove set has at least one said groovewhich communicates said fluid onto said seal ring.
 14. Thecircumferential seal system of claim 1, wherein at least one said grooveset communicates said fluid onto each said ring segment.
 15. Thecircumferential seal system of claim 1, wherein said seal ring includesa bore dam and a bore groove adjacent to said outer circumferentialsurface.
 16. The circumferential seal system of claim 1, wherein saidseal ring is disposed within a seal assembly.
 17. The circumferentialseal system of claim 1, wherein said circumferential seal system isdisposed within a turbine engine.
 18. The circumferential seal system ofclaim 17, wherein said circumferential seal system prevents leakageduring low or reverse air pressure conditions within said turbine engine19. A method of sealing a high pressure region from a low pressureregion separated by a runner with an outer circumferential surface and aseal ring including a plurality of ring segments disposed about saidouter circumferential surface comprising the steps of: (a) directing afluid from said high pressure region into a plurality of groove setsseparately disposed along said outer circumferential surface, each saidgroove set including at least two grooves; (b) communicating said fluidfrom at least one said groove within each said groove set onto said sealring as said runner translates with respect to said seal ring along anaxis substantially perpendicular to the rotation of said runner; and (c)generating a lift force along said seal ring with said fluid so as tomove said seal ring radially with respect to said outer circumferentialsurface.
 20. The method of claim 19, wherein said grooves within eachsaid groove set are different lengths or located along said outercircumferential surface so that at least one said groove is sufficientlylong so as to ensure said lift force before translation of said runnerand at least one other said groove is sufficiently long so as to ensuresaid lift force as said runner translates.
 21. The method of claim 19,wherein at least one said groove communicates said fluid under each saidring segment.
 22. The method of claim 19, wherein at most every othersaid groove set has at least one said groove which communicates saidfluid under said seal ring.
 23. The method of claim 19, wherein at leastone said groove set communicates said fluid under each said ringsegment.